GB2360900A

GB2360900A - Apparatus and method for reducing noise using a laser and interferometer

Info

Publication number: GB2360900A
Application number: GB0007590A
Authority: GB
Inventors: George Malcolm Swift Joynes
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2000-03-30
Filing date: 2000-03-30
Publication date: 2001-10-03
Anticipated expiration: 2020-03-30
Also published as: GB0007590D0; GB2360900B; FR2808371B1; FR2808371A1; DE10113735A1; US20020076059A1

Abstract

In accordance with the present invention, an apparatus and method is provided for reducing noise in a vehicle is provided. In one embodiment an interferometer 15 is disposed in the headrest 14 to measure the sound proximate to the drivers ears 18. The transducers used can be the ears of the driver, which can be painted with pressure sensitive paint or some kind of sensor attached to the ear. An equal and opposite sound is generated and transmitted to the ear 18 by loudspeakers 16 which are also disposed in the headrest, hence reducing the noise audible to the driver. A microphone 24 may be provided to make a separate measurement of the background noise to facilitate in noise reduction. Also provided for is the use of a tracking device for monitoring the movement of the drivers head and track the location of the drivers ears.

Description

2360900 APPARATUS AND METHOD FOR REDUCING NOISE

The present invention relates to the field of noise reduction. More specifically, the present invention relates to apparatus and a method for reducing noise in a vehicle.

The term noise can be used to refer to unwanted signals in general. These unwanted signals can take many forms, such as electromagnetic signals or sound waves. From hereinafter in this document the term noise is used to refer to unwanted sound waves.

Background noise is present almost everywhere. As town and cities become more crowded, background noise levels are reaching unprecedented levels causing people to take extreme measures to reduce the noise. Sound reducing fencing is being used along motorways to reduce noise caused by road traffic. Double-glazed windows are used in most modem houses to reduce street noise.

Similarly, background noise is a problem for drivers of cars and lorries. This noise comes from several sources, including the road, the vehicle's engine, other vehicles, and the wind. Means for reducing this background noise has been investigated for a considerable period of time, with limited success.

The two main approaches to noise reduction in general can be classified as passive and active methods.

Passive noise reduction methods use design and material technology to reduce the amount of noise being emitted from the source. Passive methods also includes absorbing or reflecting what remains of the noise to minimise the amount that is audible to, for example, the vehicle's driver and passengers. A further passive method is to cover or seal a person's ears with, for example, ear 2 plugs. The passive approach to noise reduction has had some success, albeit at considerable expense. Furthermore, passive noise reduction methods put undesirable limitations on the vehicle's design and may be inconvenient to the user.

The second approach to noise reduction is active noise control. This involves the use of acoustic transducers and electronic systems to create spaces, usually of a limited size, within which the noise is sampled and an equal and oppositely polarised cancellation sound is introduced. Both feedback and feedforward techniques can be used to achieve active noise cancellation. The key requirements to achieving good active noise cancellation are either to be able to measure the noise in the vicinity of the cancellation space or derive an accurate estimate of the noise by an independent means, to generate an accurate replica of the noise, and to deliver this replica to the cancellation space without exacerbating noise problems in other areas.

It is known that active noise control can be achieved over a volume that is small in relation to the wavelength of the interfering sound. Thus for a narrowband noise signal, the cancelling signal is opposite in phase with the interfering sound. As the distance between the point of maximum cancellation and the sample point increases, the phase difference moves from 180 degrees and a very rapid fall off in cancellation effectiveness occurs either side of the 180 degree point. The same principle applies to a wideband noise signal, although the worst performance will be achieved at the highest end of the frequency band.

The amount of cancellation that is needed will vary between applications. For example, human hearing considers a reduction of 1 OdB (decibel) in sound level to correspond to a subjective halving of the sound level. Thus, a 20dB reduction in sound will provide a significant and noticeable reduction in noise.

However, to achieve this over a bandwidth of 3kHz requires the sample point to be no more than 1.7mm from the point of maximum cancellation. This present a technical problem.

Currently, this technical problem of having to place the sensor close to the cancellation point has been addressed in two ways. The sensing device, such as a microphone, can be placed very close to the volume where maximum cancellation is required. Alternatively, predictive techniques are used which allow several measurements to be made away from this volume.

The first of these known approaches suffers from the need to mount a microphone obtrusively with respect to the cancellation volume. For instance, if the noise reduction is to be achieved for normal audio frequencies in a passenger's ears, the microphones have to be placed very close to the ear canal of each ear. Ideally, the cancellation should take place at the eardrum itself, but it is thought that because the canal is like a waveguide, with little dispersion, it is sufficient to do the cancellation at the entrance to the ear canal. However. this approach is often unacceptable due to the obtrusive nature of the microphones.

The second of these known ways is to use predictive techniques which enable the sensing of the sound signal to be made at a point or points remote from the cancellation volume. The problem with this approach is that the ability to predict the required cancellation signal is severely influenced by any changes in the geometry or characteristics of the environment, and thus will only work in rather simple and well controlled envirownents.

Thus, there is a need to find a way of achieving a consistently high degree of cancellation over as much of the audio band as possible,, using a technique that does not require mechanical access to the entrance to the ear canal, or use unreliable predictive techniques.

4 It is an object of the present invention to provide a reliable apparatus and method for reducing noise in a vehicle, which is both cost effective and is not obtrusive to the driver or passengers of the vehicles.

It is a further object of the present invention to provide an apparatus and method for reducing noise in a vehicle which relies on remotely measuring the sound pressure variations in the vicinity of the ear canal in order to obtain the information needed to generate a noise cancellation signal.

According to the present invention there is provided apparatus for reducing noise in an area, comprising a transducer disposed at a first location and arranged to transduce sound substantially in said area into a signal which is measurably by a measuring device, said measuring device being disposed at said first location or at a second location and coupled to a sound cancellation device, said sound cancellation device being configured to generate a cancellation signal of approximately an equal intensity and opposite polarity to the said measurably signal and to transmit said cancellation signal to said area thereby substantially reducing the amount of noise audible in said area.

The first location may be in or proximate to said area.

The second location may be remote from said area.

The predetermined location may be proximate to a human ear.

The transducer may be human skin. The skin may be part of a human pinna. The skin may be the concha. The skin may be the cavum.

The transducer may be painted with pressure sensitive paint.

The transducer may be a sensor. The sensor may be arranged to generate a voltage in response to sound. Alternatively, the sensor may be arranged to generate a magnetic field in response to sound.

The measuring device may be an optical device, such as an interferometer. The interferometer may use a laser as a light source.

The measuring device may be arranged to measure a voltage. Alternatively, the measuring device may be arranged to measure a magnetic field.

The apparatus may further comprise a tracking device arranged to search for said transducer,- to acquire a location of said transducer, and to track said location of said transducer, said tracking device being flulher arranged to communicate said location of said transducer to said measuring device.

The tracking device may be disposed in a headrest. The tracking device may be a video tracking device.

The apparatus may finiher comprise a further measuring device disposed remote to said area and arranged to measure background noise remote to said area,, said background noise being communicated to said sound cancellation device to facilitate reducing the amount of noise audible in said area.

The further measuring device may be a microphone.

The apparatus may further comprise a filter disposed between said measuring device and said cancellation device and arranged to pass a range of frequencies, thereby enabling said apparatus to cancel noise based on a frequency of said noise.

The area may be in a vehicle.

According to the present invention there is provided a method for reducing noise in an area, the method comprising the steps of transducing sound in said area into a signal, measuring said signal from a location remote to said area, generating a signal of approximately an equal intensity and opposite polarity to 6 said measured signal, and transmitting said generated signal to said area, thereby substantially reducing the amount of noise audible in said area.

The method may comprise the further step of measuring background sound remote to said area, and using said measurement of background sound to facilitate the reducing the amount of noise audible in said area.

While the principal advantages and features of the invention have been described above, a greater understanding and appreciation of the invention may be obtained by referring to the drawings and detailed description of a preferred embodiment, presented by way of example only, in which;

Figure 1 is a diagram of the preferred embodiment of the present invention, Figure 2 is a top view of the embodiment shown in Figure 1, Figure 3 shows the basic architecture of the preferred embodiment, Figure 4 shows some of the parts of a human ear, Figure 5 is a circuit diagram of a basic cancellation system for use in the preferred embodiment, and Figure 6 is a circuit diagram of a more complex cancellation system for use in the preferred embodiment.

In Figure 1, a person 10 who may be a driver or a passenger of a vehicle (not shown) is seated in a seat 12. A headrest 14 is moveably attached to the top of the seat and is disposed behind the persons head. The location of the headrest is such that a sound measuring device 15 can remotely measure the sound levels proximate the person's ear 18. A sound cancellation device 16 is also disposed in the headrest. The sound cancellation device is configured to generate a cancellation signal of approximately an equal and opposite polarity to the signal measured by the sound measuring device and to transmit this cancellation signal 7 towards the car 18. This has the effect of substantially reducing the amount of noise audible by the ear. The sound cancellation device is preferably a loudspeaker.

Also disposed in the headset is a tracking device 17 which is arranged to track the location of the ear 18 and to communicate this information to the sound measuring device 15. The tracking device may also communicate with the sound cancellation device 16. Various types of tracking devices, for example, a video tracking device could be used. The use of video devices to search, acquire and track a target is well known and as such not explained here in detail. The tracking device may require an initial set up step prior to normal operation.

In Figure 2, where parts also appearing in Figure 1 bear identical references,, a pair of sound measuring devices 15a. and 15b, a pair of sound cancellation devices 16a and 16h and a pair of tracking devices 17a and 17b, are shown. The sound measuring devices are arranged to measure the sound levels proximate each of the person's ears 18a, 18b. The tracking devices are arranged to track the movement of the head 11 and to communicate this movement to the sound measuring devices. The sound measuring devices are further arranged to be adjusted so that sound can be measured at substantially the same location. regardless of any movement of that location. Advantageously, this facilitates the continuous measurement and cancellation of noise.

In Figure 3, where parts also appearing in Figures 1 and 2 bear identical references,, the basic noise cancellation system 20 is shown comprising sound measuring device 15 arranged to remotely measure the sound pressure variations in the vicinity of the ear canal 19. The measuring device is in communication with a processor 26 via a conductor 22. The processor is arranged to interpret the sound measured by the measuring device and to calculate the appropriate 8 noise cancellation signal accordingly. The cancellation signal is then transmitted along a conductor 21 to the sound cancellation device 16, where the appropriate cancellation sound is generated and transmitted towards the car.

The cancellation system may also include a microphone 24 arranged to provide an independent measurement of the background noise. The microphone is in communication with the processor 26 via a conductor 23. The background noise information provided by the microphone is used by the processor to facilitate calculation of the noise cancellation signal. The processor 26 may include either of the circuits to be described in Figures 5 and 6.

In order for the sound measuring device 15 to remotely measure the sound in the vicinity of the ear canal, a local transduction process must occur whereby the pressure variations caused by sound is transformed into a signal which can be measured remotely by the measuring device. This may be achieved in a van ety of ways. In the preferred embodiment the sound measuring device is used to remotely access the vicinity of the ear canal. This is preferably mounted in the headrest 14 located at the top of the seat 12. Alternatively, the sound measuring device can be mounted in part of the body of the vehicle, for example, in the vehicle's doors.

The sound measuring device 15 is preferably at optical device, such as an interferometer. The operation of interferometers is well known to the skilled person and as such not explained here in detail. As is well known, an interferometer has a light source. In the preferred embodiment of the present invention this light source is a laser.

As is well known, skin will vibrate when exposed to sound waves. In the present invention the interferometer is arranged to measure the vibrations in the skin proximate to the ear canal, thereby determining the sound present at that 9 location. As will be clear to the skilled man, the path from the interferometer to the location on the skin where the measurement is made must be substantially free from obstructions, such as hair or clothing.

In Figure 4, an ear 18 is shown comprising an ear canal 19, a pinna 42, a concha 44, and a cavum. 46. In the preferred embodiment the transduction process is a natural transduction whereby sound causes vibration of the skin in the pinna, the concha, and/or the cavum. The tracking device 17 is arranged to search, acquire and track the position of the pinna, concha, and/or cavum. The tracking device is further arranged to communicate this tracking information to the sound measuring device 15 so that the sound measuring device can measure the sound at any or all of these locations on the ear. Advantageously, this natural transduction process is entirely unobtrusive to the driver or the passenger of the vehicle.

In an enhanced embodiment of the present invention, pressure sensitive paint is applied to the ear either directly or via a thin sheet disposed contiguous to the pinna, concha, and/or cavum. This enhanced embodiment functions much the same way as the natural transduction process described above, however, the sound measuring device now detects vibrations of the skin covered with the pressure sensitive paint. Advantageously, this enhanced embodiment is more sensitive than if no pressure sensitive paint were used, and is also unobtrusive.

In an alternative to the preferred embodiment a small disk-shaped sensor is located proximate to the ear canal. The sensor is responsive to sound and vibrates accordingly. The sensor may be worn by the driver or passenger as a fashion accessory, for example, as earrings. Advantageously, this alternative embodiment provides greater sensitivity than the natural transduction process previously described.

In yet a further alternative embodiment of the present invention the small disc-shaped sensor is arranged to transduce sound pressure variations into a voltage and the sound measuring device is configured to remotely measure voltage in the vicinity of the ear canal.

Alternatively, the small disc-shaped sensor is arranged to transduce sound pressure variations into a magnetic field and the sound measuring device is configured to remotely measure via induction the magnetic fields in the vicinity of the ear canal.

As will be appreciated, the use of pressure sensitive paint or sensors helps to better define the sound measurement area. Advantageously, a better defined sound measurement area reduces the requirements of the tracking device.

In Figure 5, where parts also appearing in Figures 1-3 bear identical references, the circuit diagram 50 provides the basic noise cancellation function using a simple feedback loop arrangement. The sound measuring device 15, which may be a microphone, is arranged to measure noise 55. The microphone is connected to a filter 65 via conductor 22. The filter is connected to an amplifier 52 via conductor 24. The amplifier is connected to an inverter 51 and then to a loudspeaker 16 via conductor 2 1. The filter functions to select which noise is passed on to the amplifier and the inverter and subsequently cancelled by the cancellation signal. The selection can be based on the spatial or spectral characteristics of the sound. For example, the filter may be a low pass filter allowing low frequency sound such as road noise to pass and subsequently be cancelled by the cancellation signal. High frequency sound such as voices in not passed by the filter and thus not cancelled by the cancellation signal. The inverter 51 functions to change the phase of the signal by 180 degrees which forms the cancellation signal. This cancellation signal is then transmitted by the 11 loudspeaker as a sound wave towards area 80. The result is that in area 80 the noise measured by the microphone will be substantially reduced. As will be appreciated, the area 80 preferably corresponds to the location of one of the driver's or passenger's ears.

In Figure 6, where parts also appearing in Figure 5 bear identical references, the circuit diagram 60 provides a more advanced noise cancellation fimction. The circuit 60 also uses the known HowellsApplebaum. cancellation loop. This circuit includes, in addition the features shown in Figure 5, a correlator 61 comprising a multiplier 71 and an integrator 72. The microphone 15 is connected to the correlator via conductor 22. The correlator is connected to an automatic gain control 51 via conductor 54. The gain control is connector via conductor 53 to an amplifier 52. The amplifier is connected to the inverter 51 which is connected via conductor 21 to a loudspeaker 16. The gain control functions to adjusts the gain and phase as a function of frequency of the signal output from the correlator. This signal is then inverted 180 degrees by the inverter to form the cancellation signal which is then transmitted by the loudspeaker as a sound wave towards area 80. The result is that in area 80 the noise measured by the microphone 15 will be substantially reduced.

The circuit may include a further microphone 24 which functions to independently measure the background sound 57. The further microphone is coupled to the correlator 61 via conductor 23. Disposed between the further microphone 24 and the correlator is a second filter 66. This filter functions to select which background noise is passed on to the correlator and subsequently cancelled by the cancellation signal. The filter 66 functions the same way as the filter 65 described above.

12 As will be appreciated, the gain control 51 may also include a delay means which advantageously compensates for any time delays caused by the use of two spatially distinct microphones.

The filters 65 and 66 may differ depending on the application. For example, the filters for a passenger's cancellation apparatus may be arranged such that all noise in cancelled. However, the filters for a driver's cancellation apparatus may be arranged such that all noise except for sirens, horns and the like are cancelled.

In an enhancement to the circuit 60. an independent signal, such as that from a radio 90, is input via conductor 9 1. This signal in summed with the output of the correlator and transmitted via the loudspeaker to the area 80. Advantageously, this allows for wanted signals, such as music from the radio to be efficiently transmitted to the area 80.

As will be appreciated by those skilled in the art, various modifications may be made to the embodiments hereinbefore described without departing from the scope of the present invention. For example, the apparatus and method could be used to reduce noise in a house or office, as well as in vehicles. The vehicle may be a road vehicle or an aircraft. The present invention may be used for safety purposes as well as for comfort. For example, certain types of vehicles such as tanks and tractors could use the present invention to reduce harmful levels of noise.

13

Claims

1. Apparatus for reducing noise in an area, comprising a transducer disposed at a first location and arranged to transduce sound substantially in said area into a signal which is measurably by a measuring device, said measuring device being disposed at said first location or at a second location and coupled to a sound cancellation device, said sound cancellation device being configured to generate a cancellation signal of approximately an equal intensity and opposite polarity to said measurably signal and to transmit said cancellation signal to said area thereby substantially reducing the amount of noise audible in said area.

2. Apparatus as claimed in Claim 1, wherein said first location is in or proximate to said area.

3. Apparatus as claimed in any preceding Claim, wherein said second location area is remote from said area.

4. Apparatus as claimed in any preceding Claim, wherein said area is proximate to a human ear.

5. Apparatus as claimed in any preceding Claim, wherein said transducer is human skin.

6. Apparatus as claimed in Claim 5, wherein said human skin is a part of a human pinna.

14

7. Apparatus as claimed in any of Claims 5-6, wherein said transducer includes pressure sensitive paint.

8. Apparatus as claimed in any of Claims 1-4, wherein said transducer is a sensor.

9. Apparatus as claimed in Claim 8, wherein said sensor is arranged to generate a voltage in response to sound.

10.Apparatus as claimed in Claim 8, wherein said sensor is arranged to generate a magnetic field in response to sound.

1 1.Apparatus as claimed in any of Claims 1-8, wherein said measuring device is an optical device.

12.Apparatus as claimed in Claim 11, wherein said optical device is an interferometer.

13.Apparatus as claimed in Claim 12, wherein said interferometer comprises a laser as a light source.

14.Apparatus as claimed in Claim 9, wherein said measuring device is arranged to measure said voltage.

15.Apparatus as claimed in Claim 10, wherein said measuring device is arranged to measure said magnetic field.

16.Apparatus as claimed in any preceding claims, wherein said apparatus further comprising a tracking device arranged to search for said transducer, to acquire a location of said transducer, and to track said location of said transducer, said tracking device being further arranged to communicate said location of said transducer to said measuring device.

17.Apparatus as claimed in Claim 16, wherein said tracking device is disposed in a headrest.

18.Apparatus as claimed in any of Claims 16-17, wherein said tracking device is a video tracking device.

19.Apparatus as claimed in any preceding claim, wherein said apparatus ftirther comprising a further measuring device disposed remote from said area and arranged to measure background noise proximate to said area, said background noise being communicated to said sound cancellation device to facilitate reducing the amount of noise audible in said area.

20.Apparatus as claimed in Claim 19, wherein said further measuring device is a microphone.

16 2 I.Apparatus as claimed in any preceding claim, wherein said apparatus flarther comprising a filter disposed between said measuring device and said cancellation device and arranged to pass a range of frequencies, thereby enabling said apparatus to cancel noise based on a frequency of said noise.

22.Apparatus as claimed in any preceding claim, wherein said area is in a vehicle.

23.A method for reducing noise in an area, the method comprising the steps of. transducing sound in said area into a signal, measuring said signal from a location remote from said area, generating a signal of approximately an equal intensity and opposite polarity to said measured signal, and transmitting said generated signal to said area, thereby substantially reducing the amount of noise audible in said area.

24.A method as claimed in Claim 23, comprising the further step of measuring background sound remote to said area, and using said measurement of background sound to facilitate the reducing the amount of noise audible in said area.

25.Apparatus for reducing noise as hereinbefore described with reference to the accompanying figures.

1-7 Amendments to the claims have been filed as follows 1. A - aratus for reducing noise in an area proximate anear of an observer, ^FP.comprising: - a. transducer arranged to duce noise sound substantially in said area into a signal; - a measuring device arranged to measure thesignal from the transducer, - a sound cancellation device configured:

- to receive information from the measuring device; - to generate a canoellation sound of approximately an equal intensity and opposite polarity to said noise sound; and - to transmit said cancellation sound to said area thereby substantially reducing the amount of noise sound audible in said area by said observer, characterised in that: the transducer is mounted on the body of the observer, the measuring device is remote from the transducer, and the transducer wire-lessly transmits the signal, representing sound in the vicinity of the ear canal, to the measuring device.

2. Apparatus according to claim 1 wherein the wim-less mission of the signal talws the form of light reflected from the transducer, and said measuring device is an optical device.

3. Apparatus as claimed in any of Claims 1-2, wherein said transducer includes pressure sensitive paint.

4. Apparatus amording to Claim 3 wherein the transducer comprises a pressure sensitive paint applied to the sIdn of the observer.

5. Apparatus as claimed in any of Claims 1-2, wherein said transducer is human sldn.

6. Apparatus according to Claim 4 or Claim 5 wherein the sIdn forms part of the ear of the observer.

7. Apparatus as claimed in Claim 6, wherein said sIdn is a part of a human pinna; concha; andlor cavum.

8. Apparatus as claimed in any of Claims 2-7, wherein said optical device is an interferometer.

9. Apparatus as claimed in Claim 8, wherein said interferometer comprises a laser as a light source.

10. Apparatus as claimed in Claim 1, wherein said ucer is a sensor.

11. Apparatus as claimed in Claim 10, wherein saidsensor is arranged to generate a voltage in response to sound, and said measuring device is arranged to measure said voltage.

9 12. Apparatus as claimed in Claim 10, wherein said sensor is arranged to - generate a magnetic field inresponse to sound, said wireles, transmission is a magnetic field, and said measuring device is arranged to nwastire said magnetic field.

13. Apparatus according to any of Claims 10-12 wherein the transducer comprises a sensor embedded in an item of jewellery for wearing on the ear of the observer.

14. An item of jewellery, for wearing on or proximate the ear, comprising a transducer for use in a system aocording to any of Claims 1-12.

15. Apparatus, or an item of jewellery according to claim 13 orclaim, 14, W1herein the item of jewellery is in the form of an earring.

16. Apparatus as claimed in any of-clairns 1-13, or 15, wherein said apparatus further comprises a filter disposed between said measuring device and said canoellation device and arranged to pass a range of frequencies, thereby enabling said apparatus to cancel noise sound based on a frequency of said noise.

17. Apparatus as claimed in any of iclaims 1-13, 15 or 16, wherein said apparatus further comprising a tracking device arranged to search for said transducer, to acquire a location of -said transducer, and to track said location of said transducer, said tracking device being further arranged to communicate said location of said transducer to said measuring device.

18. Apparatus as claimed in Claim 17, wherein said tracking device is disposed in a headrest.

19. Apparatus as claimed in any of Claims 17-18, wherein -said tracking device is a video tracking device.

20. Apparatus as claimed in any of-claims 1-13, 15-19, wherein said apparatus further comprises a further measuring device disposed remote from said area and arranged to measure background noise proximate to said area, said background noise being communicated to said sound=cellation device to facilitate reducing the amount of noise audible in -said area.

21. Apparatus as claimed in Claim 20, wherein said flu-ther measuring device is a microphone.

22. A method for reducing noise in an area proximate an ear of an observer, the method comprising the steps of.. transducing noise -sound in said area into a signal, measuring said signal generating a sound of approximately an equal intensity and opposite polarity to said measuwd sound, and transmitting said generated sound to said area, thereby substantially reducing the amount of noise audible in said area, characterised in that the method further comprises:

using a transducer mounted on the body of the observer; and wire-lessly transmitting the signal from the transducer to a remote measuring device.

23. A method according to claim 227 wherein the wire-less transmission of the signal is achieved by the reflection of light from the transducer, for measurement in an optical device.

24. A method as claimed in any of Claims 22-23, wherein said reflection comprises reflection from pressure sensitive paint.

25. A method according to Claim 24 further comprising the step of applying the pressure sensitive..paint to the sidn of the observer, for use as the transducer.

26. A method as claimed in any of Claims 22-23, wherein human sidn is used as the transducer.

27. A method according to Claim 25 or Claim 26 wherein the skin of the ear of the observer is used as the transducer.

28. A method aselaimed in Claim 27, wherein the sidn of a human pi concha; andior cavum is used as the transducer.

29. A method as claimed in any of Claims 22-28, wherein the fight is measured in an interferometer.

30. A method as claimed in Claim 29, wherein a laser is used as a light source for emitting light for reflection by the transducer.

3 1. A method as claimed in Claim 22, wherein said transducer is a sensor.

32. A method as claimed in Claim 3 1, wherein said sensor generates a voltage in response to the sound, and a measuring device measures said voltage.

33. A method as-claimed in Claim 3 1, wherein said sensor generates a magnetic field in response to the soundL the wireless mission is performed by a magnetic field, and a measuring device measures s aid magnetic field.

34. A method according to any of Claims 31-33 wherein the transducer is embedded in an item of jewellery for wearing on the ear of the observer.

35. A method as claimed in any of Claims 2-2-34, further comprising filtering between a measuring device and said cancellation device to pass a range of ftequencies, thereby enabling said apparatus to cancel noise sound based on a frequency of said noise.

36. Apparatus as claimed in any of claims 22-35, further comprising tracking by searching Sor said transducer, acquiring. a location of said transducer, tracking said location of said transducer, and communicating said location of said transducer to said measuring device.

37. Apparatus as claimed in Claim 36, wherein said tracking is performed by a video tracking devioe.

38. A method as claimed in Claims 22-37, comprising the fluffier step of measuring background -sound remote to said area, and using said measurement of background sound to facilitate the reducing the amount of noise audible in said area.

39. Apparatus for reducing noise as hereinbefore described with reference to the accompanying figures.